Method of and apparatus for operating electric discharge lamps in series



Oct. 1936. T. E. F'OULKE 2,056,661

METHOD OF AND APPARATUS FOR OPERATING ELECTRIC DISCHARGE LAMPS IN SERIESFiled July 15, 1934 INVENTOR 6 ATTORNEY Patented Oct. 6, 1936 METHOD OFAND PATENT caries Armm'rus son oran- ATING ELECTRIC DISCHARGE LAMPS 1NSERIES Ted a. Foulkc, Nutlcy, N. 1., assignor to General Electric VaporLamp Company, Hoboken, N. .L,

a corporation'of New Jersey- Application July 13, 1934, Serial No.735.067

' 5 Claims. (Cl. 176-124) The present invention relates to electricgaseous discharge devices generally. and in particular to the operationof a plurality of such devices in series on a constant potential system.

A particular object of my invention is-to increase the luminousefficiency of electric gaseous discharge devices. Another object of myinven tion is to provide a method of and means for op- I might be put toa more profitable use when some" crating a plurality of such devices inseries on a circuit whose potential is less than the total individualbreakdown potential of said devices. Still other objects and advantagesof my invention will appear from the following detailed speciflcatlon orfrom an inspection of the accompanying drawing. The invention consistsin the new combination of elements and in the novel steps of the methodhereinafter set-forth and claimed.

All gaseous discharge devices operating on a constant potential circuitrequire a series impedance to stabilize the discharge, as is well known.In the case of many of these devices, such as cathode glow lamps, forexample, a resistance is ordinarily employed for this purpose. Thisreslstance, however, consumes energy which might well be utilized in theproduction of light. if possibie, and with the lower dischargemaintaining voltage resulting from the improvements in electrodesurfaces which have been achieved in the last few years an everincreasing amount of energy has been dissipated in these resistanceswhich way of utilizing .it was found. With this improvement in theelectrode surfaces there was, of course, a corresponding decrease inbreakdown potential, but this potential is still too high to insuresatisfactory operation of two of these devices in series on the usual110 volt circuits, hence this mode of decreasing the wasted energy hasnot been available heretofore.

I have now discovered, however, that two of these improved cathode glowlamps can be operated in series on any 110 volt A. C. line with,

complete success, despite'anyusual line voltage fluctuation, provided a.novel means of my in vention is utilized to unequally distribute theline potential between the lamps at starting, causing the lamps to breakdown in turn. With this novel arrangement the breakdown potential of thecombination is no longer the sum of the individual breakdown potentials,as heretofore, but instead is the breakdown potential of one plus themaintaining potential of the other. This difference is just enough tosecure satisfactory operation of the lamps under all conditions on a andnovel 110 volt circuit. According to my invention this, new result isobtained by bridging the terminals of one of the lamps with a resistanceor other impedance of the order of 100.000 ohms, this re- 'sistancerobbing the bridged lamp of potential 5 and thus applying-the entireline potential to the other lamp until a discharge is started therein.This resistance thereupon consumes considerably more than half of theline potential, thus raising the potential across the bridged lampsuiliclently 10 to initiate the discharge therein. The two lampsthereupon continue to operate in series with virtually no current flowthrough the high resistonce. The series ballasting resistance is, ofcourse, reduced to a small value due to the presl5 cues of the secondlamp, and the luminous elliciency of the combined unit is not onlydoubled as compared to a single lamp as a result thereof, but is alsogreater than would be possible with the simple connection of two lampsin series, due 90 to the decrease in the voltage required to operate mynovel combination of lamps.

For the purpose of illustrating my invention I have shown a preferredembodiment thereof i the accompanying drawing, in which Fig. l is anelevational view showing two cathod glow lamps of a well known typecombined in a single mounting unit for series operation, and

Fig. g is a schematic diagram showing the elec-- trical connections ofthe same unit.

As shown in this drawing a pair of identical cathode glow lamps I and 2are cemented within opposite ends of a suitable insulating base 8 havingplug contacts 4 and 5 on the bottom thereof.

Each glow lamp has a pair of electrodes 6 and 'I which are suitablysupported on the inleads 8' and 9, respectively. These glow lampscontain any suitable gas or vapor or mixture thereot at a relatively lowpressure. For example, in some cases I preferto use a mixture of neonwith .05 to 5% 40 of argon at a pressure ofthe order of 20 to 50 m. m.of mercury. The electrodes 8 and 1 are each preferably coated on theconvex face thereof with barium and strontium with an oxygen bond,

as disclosed in my Patent 1,965,589, issued July 10, 1934, since thiscoating has been found to provide both low work function, with acorrespondingly low breakdown potential, and long life. The concave sideof each of these electrodes is preferably coated with finely dividedaluminum in order to keep the glow from covering this part of thesurface, where the light could not be utilized. .This aluminum alsoserves as a getter as the result of the treatment it receives during theman- 5 g ufacture of the lamp, and thus cleans up any undesiredimpurities.

Within the socket I the connections are as follows. The plug contact 4is connected to the inlead 8 of the lamp I. while the other plug contactI is connected to the inlead 8 of the lamp 2. The lnlead 9 of lamp l isconnected to the inlead l of the lamp 2 through a resistance IU of theorder of 600 to 700 ohms. The exact position of this resistance is of noparticular importance, so long as it is connected in series, and in somecases it may be divided and the halves directly associated with thelamps i and 2. Other forms of impedance may likewise be employedwhere'desired. A resistance ll, of the order of 100,000 ohms, isconnected between the inleads 8 and I of the lamp l.

In the use and operation of the lamp combination illustrated as soon-asthe plug terminalsare connected to a suitable source of supply, such asa nominal 110 volt A. C. line, the entire line voltage is impressedbetween the electrodes 8 and I of the lamp 2. due to the fact thatthere,is no voltage drop in either of the resistances ID or so long asthere is no current flow therethrough. The glow lamp 1 has a breakdownpotential, however of the order of to volts A. C.. if it is made ashereinbefore described. and hence the impressed potential immediatelyinitiates the discharge therein. This discharge is limited to a smallvalue, however, by the resistance I I. which now consumes virtually allof the line potential less the maintaining potential of the lamp .2.Since the latter is of the order of 40-45 volts it is apparent that thisresistance drop, which is like-'" wise the potential now impressedbetween the electrodes 6 and I of the lamp I, is of the order of '65-'70volts, and in some cases an even higher voltage can be obtained by useof a condenser in place of the resistance ll, due to the shift in phaserelations. The lamp I has a breakdown potential, however, of but 50-55volts, and hence the discharge is now initiated in this lamp. Thecurrent in both lamps then increases to the limit set by the ballastresistance l0, this current being about .027 amperes in the casedescribed and illustrated. The resistance ll, due to its relatively highvalue, carries but little of this current, so that both lamps glow withsubstantially the same brilliancy. It will be noted that with this novelarrangement suillcient tolerance is provided so that the line voltagecan drop from the nominal 110 volts to volts or even less, and both ofmy novel lamps will still start and operate satisfactorily, although inthe absence of the resistance l l these same lamps will fail to operateas soon as the potential drops appreciably below the nominal voltage of110. Thus in an actual case two lamps which required a minimum of voltswhen merely connected in series would operate satisfactorily on 8'1volts after the resistance II was added. From this it will be apparentthat it is only through my novel use of a bridging resistance orimpedance that these lamps can be satisfactorily operated in series, foron most lines there" is a greater deviation from the, nominal voltagethan these lamps could otherwise tolerate. As

aos0,001

a result of novel arrangement I now find it possible to obtain doublethe luminous eiliciency which has heretofore been attainable with theselamps withouflaltering the operating conditions i of the lamps in anyway.

While the above description has been limited to. the use of two lamps inseries on A. C. it is to be understood that it is also applicable to theuse of such lamps in series on D. C. if desired. although 220 volts D.C. isordinarily employed for this purpose. It is also to be understoodthat more than two lamps can be connected in series with advantage insome cases, as where 220 volts D. C. is employed, with one of the lampsby-passed as described during starting, and that other types of gaseousdischarge devices than that described may likewise be started andoperated in series on a lower voltage by the aid of my novel circuit.Various other changes, substitutions, and omissions, within the scope ofthe appended claims, may also be made in the structure illustratedwithout departing from the spirit of my invention.

I claim as my invention:

i. In combination, a plurality of electric gaseous discharge devicesconnected in series, and a single impedance permanently connectedbetween the terminals of a single one of said devices whereby theremaining devices receive more than their proportionate share of anapplied potential before a discharge is initiated therein.

2. In combination, a plurality of electric gaseous discharge devicesconnected in series, and a single resistance permanently connectedbetween the terminals of a single one of said devices whereby theremaining devices receive more than their proportionate share of anapplied potential.

before a discharge is initiated therein.

3. In combination, a plurality of cathode glow lamps connected inseries, and an impedance con- 1 nected between the terminals of a singleone of said lamps, said impedance having a value greater than theapparent impedance of one of said lamps after a discharge is initiatedtherein whereby theremaining lamps first receive more than theirproportionate share of an applied potential before a discharge isinitiated therein, and then less than their share until a discharge isinitiated in said single lamp.

4. In combination a socket adapted to retain a plurality of electricgaseous discharge devices and to connect said devices in series, animpedance within said socket to stabilize the current through saiddevices, and means comprising another impedance within said socket andconnected in multiple with one of said devices to provide an unequaldistribution of an applied potential on said devices before a dischargein each one thereof.

5. The method of starting and operating a plurality of electric gaseousdischarge devices in series which comprises applying line potential toall except one of said lamps in series through-an impedance to initiatea discharge in said lamps, and thereafter applying the voltage drop insaid impedance across the excepted lamp to initiate a TED E. FOULKE.

